Hi there, so when I plug in my bass to my LD 15 and turn on the amp it just produces this really loud, horrible noise. The best I can describe it is its very loud, continuous, and has lots of both treble and bass. Its like the sound that's made when you plug a cable running from an amp into an instrument when the amp is already turned on, only much louder and continuous. When the volume is all the way down this doesn't happen but the sound gets exponentially louder as the volume is only slightly turned up. Any assistance please? Thank you